1. Field of the Invention
This invention relates to a rotary hydraulic motor, preferably a ring gear motor, comprising a brake, which is adapted to be applied under the pressure of springs and to restrain the output shaft of the hydromotor when the hydromotor is not pressurized and which is arranged to be lifted by a hydraulic cylinder in response to a supply of hydraulic liquid under pressure to the hydraulic motor.
2. Description of the Prior Art
In rotary hydraulic motors used to drive winches or grabs, it is desirable and often necessary to restrain the motor shaft by the brake when the hydraulic motor is not pressurized so that it does not deliver an output torque.
It is known per se that the motor shaft can be restrained by a brake, which is biased by compression springs, and to lift the brake in that the compression springs are compressed by a hydraulic cylinder when the motor is started by a supply of hydraulic liquid under pressure. That hydraulic liquid is simultaneously supplied to the hydraulic cylinder for lifting the brake.
But a special problem resides in that the shutting off of the pressure line will stop the motor because it is no longer supplied with hydraulic liquid under pressure and in that case hydraulic liquid can no longer flow back from the hydraulic motor, which is substantially relieved from pressure. As a result, liquid under pressure cannot leave the brake-lifting hydraulic cylinder so that the brake will remain lifted also when the motor is at a standstill. To permit an application of the brake even when the hydraulic motor has been stopped by a shutting off of the pressure line for supplying hydraulic liquid to the motor, it is necessary to provide special means which permit a reverse flow of hydraulic liquid out of the hydraulic cylinder.